Well, this was one of the parts that was a major step in the process. You could get all screwed up here, for sure. The computer is not going to be too forgiving to incorrect connections and the motor needs the sensors to run well if at all.
I did have one major advantage, I had the entire car, a 1992 Mustang GT convertible. I did not have to work from some cut up harness that someone else pulled from a junkyard, etc. I could see how it was all routed, where it connected and to what. So, before I pulled the motor, I disco'd the wires that ran from the engine management harness to the harness for the EEC (or PCM or Brain...or whatever, the computer) and to the chassis harness. The 5.0 is pretty simple to separate. Nearly the entire harness is hooked into the 'Salt and Pepper' connections that sit behind the air plenum at the center of the firewall. Others, like the HEGO harness, wiring to the TFI/Dist., alt, and a few others are pretty straight forward. It tagged each pair of wires/connectors as I separated them and I took a bunch of digital photos to refer back to if needed.
Here are some sources I had at my disposal for reference:
Without these, I would have been lost. It pays well to understand the system, how things work, what each thing does. Maybe not a deep, engineer level type of understanding, but at least a good foundation. These books will get ya on the path and beyond.
The EEC is mounted behind the passenger kick panel in the footwell of the 1992 Mustang I have as a donor car. I found it easier to remove the entire heater/AC box and motor assembly to better get to the computer and firewall where it ran into the engine bay.
I had the entire harness cut loose in the engine bay so, I pushed the rubber plug back into the passenger footwell and began pulling the harness through into the car. It took a bit of wrangling and it needs to be done so the relays can pass through next to the harness loom, but it came out pretty easily. Note: I found out afterwards that I could have pulled the plug through into the engine bay instead, but hey, why make it easy?
There are some connections in the footwell that need to be disco'd as well. I unbolted the EEC and unplugged it so I could move the harness around more easily. The next thing I did was sit down on my kitchen floor (it was a cold day outside!) and I laid out the harness with all my reference material. I had tagged the connections with numbers or letters like A1/A1 or whatever if I did not know what they were hooked to. I knew stuff like alternator wiring, but each sensor was not clear yet. Now, I wanted to know all the details. Based on what I could devine from all the notes, I took pics of each wiring section and noted the connector use and wiring colors. I have not actually hooked it up and gotten anything to run, so take this as good suggestions, not gospel...yet. I will update as it goes along. The Section call outs are links to more details.
OK, next I will begin to place it all in the Jeep. Stay tuned.
Updates: 02/07
Now, the goal of any wiring project is to have it not only work, but look clean, organized, and be reliable. I looked at how the Ford EEC harness would lay out in the YJ. Some things to consider are the Mustang battery and power circuits are on the drivers side and the YJ's were on the passenger side. Also, I wanted to keep any connections between the Ford engine harness and the EEC harness in the same locations so that wires would fall into place with no cutting and splicing (or as little as possible).
Now, where to bring the harness into the engine bay was the next issue. Either I could cut a new hole behind the glove box area and follow the basic layout that the Mustang had, or I could try to use the Jeep path and run it out on the drivers side of things. I looked at it for a minute and then fed the EEC plug into the existing hole in the YJ till it hit where the grommet was. I did move the grommet as far as possible towards the split in the harness to get as much tail as possible, but when it was all said and done, it looked factory and even the Ford grommet fit perfectly into the Jeep firewall.
The EEC from the Ford mounted nicely in the stock Jeep location behind the glove compartment. I even used the Jeep bracket and used a heavy duty zip tie and some foam padding between the EEC and the bracket to keep it in place as the Ford one lacked the tabs to screw it to the bracket. I also attached the black EEC ground wire which pigtails out of the EEC harness to the bracket which, in turn, grounds to the firewall.
The green 8 pin connector that is next to the EEC is a very important part of the process. If at all possible, get the other end of this plug from the donor vehicle and as much wiring as possible. Since I had the whole car, I was able to get enough of the wiring to go all the way into the engine bay without any splicing. I ran it all in high temp split loom.
I have begun to lay out and separate the engine compartment wiring into the basic sections. You can see from the pics that the Salt and Pepper 10 pin plugs sit nearly exactly where they did in the Ford. The MAF section I extended about a foot and the alt, HEGO, VSS, etc will fall pretty close to right. We shall see as I slide the engine in. The power circuits all ended up on the correct side of things as well. Those would be the easiest to extend, so if you choose to do it 180 degrees to this OR I find out it will not work this way, that would be doable. Here are some pics of how the engine bay is laying out.
I also wanted to eliminate as many of the fusible links as I could with fused circuits. I picked up a PDC (Power Distribution Center) out of a Ford Taurus with a 3.0 V6. It is a very slick deal and will allow for options for all the constant 12V powered circuits and future stuff as well. You can see where I mounted the inertia switch out of the Mustang (located in the trunk on my donor car) next to the OE wiring harness connector on the Jeep firewall. This is an option, but the inertia switch, if it does it's job, will cut power to the fuel pump in the evnt of a roll over or serious impact. I was concerned about nuisance tripping, but I read several times that if the switch is solidly mounted, it will work well. We shall see. The output of the Ford harness to the fuel pump will tie into the inertia switch and then out of the switch to the orange wire that is OE to the Jeep fuel pump.
There are excellent reasons to have the entire car for donor parts and pieces. For instance, the OE Jeep harness bundles the reverse switch (at least for my manual tranny YJ) into the connector to the 4wd system for the front axle. You can see the harness in this pic and the part I cut out to fit up to the plug out of the NV3550. It will tie into the OE Jeep wiring where it comes out of the firewall connector. I also pulled the VSS wires from under the car and kept the wiring that went into the dash harness as long as possible. These wires will tie into the green 8 pin connector wiring.
This is like eating an elephant. You do it one bite at a time. I will say that if I had not had a lot of internet info and a pretty good idea of how to figure it out, I would have budgeted for an aftermarket harness like this one and saved myself a bunch of time and trouble. Still, expect to pay $500.00 and up plus sensors for that set-up. I paid $800.00 for the whole car. I will post all the wiring connections, colors, and locations I used WHEN I know they all work. Until then, I don't want to lead you astray.
Next time, we start proving out circuits and making connections.
Swapping the EEC Harnesss into BOYJ : Wires, sensors, and plugs...oh my! Making sense of all that colored spaghetti. I hope!
By Michael Troy
